In most conventional oil or gas drilling operations, drilling takes place on a drilling platform, which in turn supports a circular rotary table. The rotary table is designed such that it can be moved in a circular fashion via standard electrical or hydraulic motors. The conventional rotary table has a “kelly” which provides the central opening or bore through which passes the drill string. The kelly itself is supplied with a bushing or “kelly bushing,” which can be interlocked with a bushing on the rotary table or “master bushing” such that the rotary table can drive the kelly and impart the needed rotational force to the drill string to effect drilling. Such well drilling equipment is conventional and well-known in the art.
To add or remove a joint of pipe from the drill string, wedge devices called “slips”, are inserted into the rotary table central opening into a bowl to prevent the drill stem from falling into the well bore. In many conventional drill platforms, placement of the slips is done manually by well personnel. Sometimes the personnel operating the various mechanical devices in proximity to the rotary table are required to remove an entire drill string from the well bore. This is a time consuming process which requires removal of individual lengths of pipe one at a time in order to completely remove the drill string. This removal necessarily requires the personnel to repeatedly disengage the slips or slip assemblies from their operative position of holding the drill string, and back into the operative position when the next section of drill pipe is in position to be removed from the drill string. As a result, at each removal or addition of a length of drill pipe from the drill string, oil well personnel are required to exert a great amount of manual physical labor to remove/replace slips, which is dangerous because of the large forces required, as well as the great amount of weight which is being handled.
To improve the efficiency and safety of the drilling operation, a “power slip” has been developed, which is rotatably retained within a slip bowl to prohibit the slips from vertical movement while the slip bowl rotates with the rotary table about the drill pipe. Such power slip mechanisms include primary components which are arranged in several basic configurations. The main structure is the slip bowl or body which is generally an enlarged support structure having an internal tapered bore. Slip elements are disposed within the bore and when allowed to fall under the force of gravity, wedge radially against the casing so as to prevent the casing from slipping downwardly. The slips and the bowl are configured such that outer surfaces of the slips contact inner surfaces of the slip bowl in sliding friction and can be automatically activated to seize and hold the drill stem when a portion of the drill stem is being added or removed. For example, such power slip arrangements have been shown in U.S. Pat. Nos. 2,570,039; 2,641,816; 2,939,683; 3,210,821; 3,270,389; 3,457,605; 3,961,399; 3,999,260; 4,253,219; and 4,333,209.
Such prior art power slips come in two basic configurations. One in which the power slip is permanently attached to and rotates with the rotary table and one in which the power slip is disconnected from the rotary table when not in use.
Of the first type, U.S. Pat. Nos. 2,641,816 to Liljestrand and 3,961,399 to Boyadjieff are examples. While these power slips do represent an advance over the conventional manually operated slips, most require permanent attachment of a support post or other structure to the rig floor at the side of the rotary table to allow the power slip to be pivoted or raised away from the frill stem. As such, these devices permanently occupy valuable drill floor space despite the fact that during much of the drill time they will not be in use and may interfere with other drilling operations.
However, in most of the early systems of the rotary power slips, a mechanical linkage had to be provided between a stationary fluid cylinder and the rotary power slip housing. In many of the early conventional systems the slip assembly could not be activated at any point in its rotation but required alignment of the stationary fluid cylinder and the rotary housing. As a result the assembly protrudes above the rig floor thus consuming valuable space. The rotary power slips disclosed in U.S. Pat. Nos. 3,999,260 to Stuckey et al. and 4,333,209 to Herst solve this problem by providing expansive seal means on the stationary fluid supply which form a fluid duct with the rotary housing during operation, eliminating the need for a mechanically aligned linkage and reducing or entirely eliminating the need to utilize valuable floor space for the power slip mechanism. However, the expansive seals provided in both of these systems have been found to be prone to leakage and rapid deterioration as a result of rig vibration, affecting the efficacy and alignment of the seal with the rotary housing. In addition, these prior art devices are prone to introducing mud and debris into the seal and pressurizing system, leading to damage of the hydraulic or pressurized air systems.
Accordingly, a need exists to provide improved rotary power slip seals, which have longer wear and more effective seals, and which provide additional protection from mud and debris entering the power slip system.